People become more and more concerned about the indoor air quality in the past decade since the national standard “Indoor Air Quality” entered into force. The pollution caused by the broadly used air-conditioners as well as building materials and furniture materials with poor quality has created a severe issue that must be addressed immediately. Currently, the PM 2.5 particle has become a major problem of indoor air pollution. Particularly, when considering the ever nationwide large areas of severe fog and haze which took place from December 4 to 7, 2013, the problem of PM 2.5 should be solved as quickly as possible. PM 2.5 refers to particles with the diameter of less than or equal to 2.5 micrometers, which can enter the people's lungs. Compared with the coarser particles, PM 2.5 particle has a smaller size, contains large amounts of toxic and hazardous substances, and can stay in the atmosphere for a long time and transport a long distance, and thus has a greater impact on human health and environmental quality of the atmosphere.
The main source of PM 2.5 comes from outdoors, it pervades everywhere due to its small size. According to the monitoring results of July and August 2013 in Beijing, indoor PM 2.5 pollution has a tendency to exceed the outdoor pollution. Since people mainly live and work in the room, the indoor PM 2.5 pollution has reached a very serious level. There are several ways to remove the PM 2.5 particles, of which the most reliable and the most commonly used method is filtration. Washing and electrostatic precipitation are also common methods. But all these dust removing methods have shortcomings. Filtration is the simplest method with a low cost. However, filtration of PM 2.5 particles requires at least medium efficient filter, which suffers a large resistance and is easily blocked, thus has to be regularly cleaned or replaced. The washing method is also easy to implement, but it produces excessive amounts of moisture that cause indoor humidity level rise which is a kind of pollution for the humid regions of the world. The electrostatic precipitation method is effective not only in dust removal, but also in antivirus sterilization; however, it produces ozone during operation, which is lethal to humans. The serious outdoor air pollution, especially the PM 2.5 pollution will be introduced indoor with the new air, thereby aggravating damage on people. The introduction of new air so as to degrade indoor pollution and to solve the problem of indoor oxygen supply is the primary task among Chinese imperatives.
The typical spread fully naked electrostatic air purifier that is widely employed employs naked metal as a generator for high electrostatic field and is one of the ideal products used for dust removal, sterilization, disinfection in health care system due to its significant effect of dust removal. However, the naked electrostatic air purifier produces too much ozone for use in closed room or places where people exit. Europe and the United States have expressly provided that the naked electrostatic air purifier should not be used in places where people exit. In order to solve the severe recurring problems of PM 2.5 pollution in China, many domestic experts specializing in electrostatics have been studying such naked metal generators. They have devised an electrostatic precipitator with circular columns as negative electrodes and acicular metal columns as positive electrodes. The electrostatic precipitator produces ozone below the national standard requirements during operation. The emission of ozone reaches 0.01 mg/m3 after startup for 40 minutes and reaches 0.16 mg/m3, the national standard value, after startup for 16 hours. When the ozone content of the room itself is taken into account, the increment of 0.01 mg/m3 per hour is still a excessive enough to be considered a source of contamination. Also, the precipitator loses suction force when power off, thereby those dust particles adsorbed on the negative electrode fall within the precipitator and will be blown into the room when the precipitator is started up again. Thus, the precipitator loses its purification function.